A new species of Apistogramma is described from Peru, based on a total of 28 specimens collected in a small forest stream in the catchment of a nameless tributary of the Rio Amazonas about 80 kilometres south of Iquitos, Departamento Loreto (approximately 73° 34′ W / 04°24′ S). At first sight Apistogramma paulmuelleri sp. n. resembles A. regani, but is differentiated from the latter and all other Apistogramma species by the combination of a large band-like spot on the caudal-fin base, four distinct abdominal stripes, a roundish, banded caudal fin, a low dorsal fin without any striking features, in adult males yellow on the chin between the gill covers and on parts of the branchiostegal membranes, ivory sides to the head below the cheeks, and reversal of the band pattern during aggression and courtship display. Apistogramma paulmuelleri sp. n. is currently thought to be a representative of the Apistogramma eunotus complex within the Apistogramma regani lineage.